Internet Protocol (IP) defines a standard by which data is transmitted over networks in the form of packets which are then routed to the intended recipients. In the past, IP data was limited to text, numbers, or simple pictures due to the constraints imposed by relatively slow and unsophisticated networks. However, as networks and routers become faster and more powerful, it has now gotten to the point where service providers are starting to offer real-time voice-over-IP (VoIP telephony) and digital television (IPTV) in addition to their standard IP-based web/Internet services. This “triple play” option of providing VoIP, IPTV, and IP Internet services over a single DSL, fiber optic, or cable line has proven to be quite popular with subscribers. Subscribers can make telephone calls, watch television, and surf the web without having to deal with a number of different companies. Presumably, the triple play option is cheaper for the consumer than if they had to subscribe to each of the services separately. And for service providers, triple play confers an opportunity to capture revenue from all three sources.
Aside from convenience and cost savings, triple play offers subscribers new features. For example, IPTV has several advantages over that of traditional TV. IPTV's point-to-point distribution scheme enables efficient stream control. Subscribers can pause, wind/re-wind, playback, skip, fast-forward, one-click recording, etc., all from the set-top box. In addition, IPTV inherently has the ability for two-way communication. This enables subscribers to select which movie they want to watch at any given time. Video on demand (VOD) is very popular with subscribers and is a growing source of revenue for service providers.
Unfortunately, video content contains a great amount of data. This is problematic because the “last mile” to/from a residence or office is typically bandwidth constrained. In other words, the last mile of twisted pair copper wires, fiber, cable, or wireless connection is physically limited to handling a maximum number of IP packets which may be transmitted over a given amount of time. IPTV can strain the capacity of the last mile, especially if other users are simultaneously surfing the web or making telephone calls or watching TV in another room.
One commonly used approach for minimizing the bandwidth requirements associated with transmitting video entails compressing the video through a video compression scheme, transmitting the smaller compressed video data, and then decompressing the video data before being displayed. A widely adopted video compression standard is set forth by the Moving Pictures Expert Group (MPEG). For instance, the MPEG-2 standard converts a video stream into I, P and B frames. The I frame is an intra-frame which contains all the data required to display the frame. An I frame is followed by a series of P and B frames. The P frame is a predictive frame which contains only the data that has changed from the preceding I frame. P frames rely on I frames to fill in most of its data. The B frame is a bidirectional frame which contains data that have changed from the preceding frame or are different from the data in the very next frame. By converting the frames of the original video stream into much smaller I, P, and B frames, the video stream comprised of I, P and B frames can be transmitted at a fraction of the bandwidth compared to non-compressed video streams. Once received, the I, P, and B frames are then used to reconstruct the original video stream for playback.
There is, however, one drawback to MPEG-2 and equivalent video compression schemes. When a subscriber switches channels, there can be a significant delay incurred in acquiring and displaying the selected new channel on the television screen. If the subscriber happens to switch channels right after an I frame was just transmitted for the new channel, the TV cannot display any video until the next I frame is received. Although a series of P and B frames are received, they are useless because a corresponding previous I frame is needed as a reference. Essentially, the viewer can occasionally experience a momentary blank or black screen right after switching channels. This can be quite disconcerting to viewers who are accustomed to traditional TV whereby switching channels instantaneously brings up the new channel for viewing.